Starting and overload control for motors



1965 w. B. WHITLER ETAL 3,164,699

STARTING AND OYERLOAD CONTROL FOR MOTORS Filed Oct. 17. 1961 INVEN T 0R5 WILLARD B.WHITLER BY ROBERT E. PROUTY AGENT United States Patent Ofitice 3,164,699, Patented Jan. 5, 1 965 STARTING AND ()VERLUAD CONTROL FUR MOTQRS Wiilard B. Whitler and Robert E. Prouty, Logansport,

ind, assignors to Essex Wire Corporation, a corporation of Michigan Fiied Oct. 17, 1961, Ser. No. 145,588 2 Claims. (Cl. zen-113) This invention relates to an electric control which may be used for controlling the starting of a single-phase alternating current motor and for overload protection of the motor, and is particularly concerned with a thermally responsive control for an electric motor of the splitphase type, the object being to provide a compact and inexpensive arrangement of simple COIlSilllCllOiL' According to this invention, the control for a sp1itphase motor comprises a spring strip connectable to a power supply conductor, a first bimetal strip connectable to the running winding of the motor, and a second bimetal strip connectable to the starting winding of the motor. The first bimetal strip is arranged to have switching engagement with either of the other two strips. The spring strip is biased to be normally in following contact with the first bimetal strip and the second bimetal strip is norrnally separated from the first bimetal strip. The bimetal strips are individually heated in response to the currents in their respective circuits and move in the same direction when heated. The first bimetal strip in response to the running winding current initially contacts the second bimetal strip to energize the starting winding. The starting winding current then shortly causes the second bimetal strip to move away from the first bimetal strip thereby reopening the starting winding circuit. The control further includes a stop located in the path of the spring strip which prevents the latter from following the first bimetal strip in the event the first bimetal strip moves beyond a predetermined position in response to a continued abnormally high current in the running winding circuit. The separation of the spring strip and the bimetal strip thus deenergizes the motor to protect it from overloading. Other objects and features of the invention will be apparent from the following description and accompanying drawing in which:

FIGURE 1 is an exploded isometric view of a control embodying the invention with portions thereof broken away;

FIGURES 2, 3, 4, and 5 are schematic elevational views of. the control shown connected to an electric motor and illustrating operation of the control.

Referring now in detail to the drawing, the parts of the control are mounted on a supporting member or base of insulating material which may be provided with a suitable cover for enclosing the parts.- The control includes two bimetal strips 11 and 12 and a conductive spring strip 13. The stationary ends of :these strips are fixed in a stack upon the thickened end or platform 14 of the base 10. Adjacent the stationary ends of the strips 11, 12, and

13 are the terminals 15,16, and 17, respectively, by which an electrical circuit may be completed to each strip. An

insulating Washer 11% is interposed between the bimetal strip 11 and the terminal 16 while a similar insulating washer 19 is interposed between the bimetal strip 12 and the spring strip 13. A hollow rivet 20 extending through an insulating bushing 21 is used to firmly secure the entire stack to the base 10.

The bimetal strip 12 carries the double-face contact 22 and a snap-action permanent magnet 23 having two sets of poles which cooperate with respective armatures 24 and 25 attached to the strips 11 and 13'. One face of the contact 22 is adapted to engage the contact 26 carried by the bimetal strip 11 while the other face of the contact 22 is adapted to engage the contact 27 carried by the spring strip 13. Both of the bimetal strips 11 and 12 are arranged to move toward the base 10 when heated. The position of the bimetal strip 11 is adjustable by means of a screw 28 threaded in the base 10 and bearing against the strip 11. The spring strip 13 is biased in the direction of the base 10 to' follow themovement of the bimetal strip 12. The free end of the spring strip 13 protrudes beyond the free end of the bimetal strip 12 for engagement with a stop screw 29 threaded in an upstanding end portion 30 of the base 10. The stop screw 29 limits the movement of the strip 13 in a direction toward the base 10 such that contacts 22 and 27 will be separated upon movement of the bimetal strip 12 in a direction toward the base 10 be yond a predetermined position. The bimetal strips 11 and 12 are preferably self-heated by the current flowing through them but it will be apparent that they may also be heated by external heating elements of suitable resistance material.

Referring now more specifically to FIGURES 2 through 5, the control is shown connected to a split-phase motor having a starting winding 31 and a running winding 32. The junction of the starting winding 31 and the running winding 32 is connected to one supply conductor 33 of a single phase alternating current power supply. The other supply conductor 34 is connectedto the spring strip 13. The-bimetal strip 11 is connected to the otherterminal of the starting winding 31 by the conductor 35 while the bimetal strip 12 is connected to the other terminal of the running winding 32 by the conductor 36.

When the bimetal strips 11 and 12 are cold, the strips 11, 12, and 13 will assume the positions shown in FIG- URE '2 with the contact 27 engaging the contact 22 and with the contact 26 separated from the contact 22. When the conductors 33 and 34 are initially energized, the cur rent flows from the conductor 33 to the conductor 34 through the running winding 32, the conductor 36, the bimetal strip 12, the contacts 22 and 27, and the spring strip 13. IAs the starting winding 31 is not energized, the current through the running winding 32 will have a high value and rapidly heats the bimetal strip 12. This causes the bimetal strip 12 to rapidly bend toward the bimetal strip 11 until the contact 22 engages the contact 26 as shown in FIGURE 3. The engagement of contacts 22 and 26 completes the energizing circuit for the starting winding 31 to the conductors 33 and 3 1 through the starting winding 31, the conductor 35, the bimetal strip 11, the contacts 26, 22, and 27, and the spring strip 13.

The current through the sarting winding 31 now rapany heats the bimetal strip 11 and after a time interval sufficient forthe motor to attain its normal running speed, the bimetal strip 11 becomes sufficiently heated to pull the armature away from the magnet 23 to the position illustrated in FIGURE 4. The separation of the contacts26 suppiies suificie'nt radiant heat to the bimetal strip 11 tomaintain the contacts 22 and 26 separated.

The parts of the control will remain generally as shown in FIGURE 4 as long as the current flow through the running winding 32 remains normal. If the current flow through the running winding 32 becomes excessive dueto an overloading of the motor, it will further heat the bimetal strip 12 and cause it to bend toward the base 15) until the spring strip 13 engages the stop screw 29. When the bimetal strip 12becornes'suficiently heated to pull the magnet 23 awayfrom the armature 25, the bimetal strip 12 will snap to the position shown in FIGURE 5 thereby separating the contacts 22 and 27. This will disconnect the running winding 32 and the motor is deenergized. Deenergization of the motor circuits allows the bimetal strips to cool and return to the positions shown in FIGURE 2.

While the invention has been illustrated and described in its preferred embodiment and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried out in other ways falling within the scope of the invention as claimed.

What is claimed is:

1. A combined starting and overload protection control for an electric motor having starting and running windings comprising: a supporting member; a conductive spring strip carrying a first contact and having a first terminal connectable to a supply conductor; a first bimetal strip carrying a double contact and having a second terminal connectable to said running winding; 2. second bimetal strip carrying a second contact and having a third terminal connectable to said starting winding; said strips being arranged to extend generally in the same direction in laterally spaced relation with said first bimetal strip being between the other two strips; each strip being supported by said supporting member at one end so that the free ends of said strips are movable relative to each other; said two bimetal strips each being arranged to move in a direction away from said spring strip when heated; said spring strip being biased to urge said first contact into engagement with said double contact when said first bimetal strip is cool and to urge said first contact into following engagement with said double contact as said first bimetal strip moves; stop means supported by said supporting member limiting following movement of said spring strip in a direction toward said second bimetal strip upon movement of said first bimetal strip beyond a predetermined position; said first biinetal strip being responsive to initial current flow therethrough to move said double contact into contact with said second contact; said second bimetal strip being responsive to current flow therethrough to move said second contact away from said double contact; said second bimetal strip maintaining said second contact separated from said double contact While heated by said first bimetal strip; said first bimetal strip being responsive to a continued abnormally high current flow therethrough to move beyond said predetermined position whereby said double contact is moved away from said first contact; and snap-actingrneans carried by said strips to effect quick engagement and separation of said contacts.

2. A control according to claim 1 wherein said snapacting meanscomprises a magnet carried by said first bimetal strip and having poles facing each of the other two strips; and said spring strip and said second bimetal strip each, carrying an armature cooperating with said poles.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,713 Hodgkins July 4, 1944 2,764,650 Hodson Sept. 25, 1956 2,984,722 Smith et al May 16, 1961 FOREIGN PATENTS 423,225 Great Britain Jan. 28, 1935 

1. A COMBINED STARTING AND OVERLOAD PROTECTION CONTROL FOR AN ELECTRIC MOTOR HAVING STARTING AND RUNNING WINDINGS COMPRISING: A SUPPORTING MEMBER; A CONDUCTIVE SPRING STRIP CARRYING A FIRST CONTACT AND HAVING A FIRST TERMINAL CONNECTABLE TO A SUPPLY CONDUCTOR; A FIRST BIMETAL STRIP CARRYING A DOUBLE CONTACT AND HAVING A SECOND TERMINAL CONNECTABLE TO SAID RUNNING WINDING; A SECOND BIMETAL STRIP CARRYING A SECOND CONTACT AND HAVING A THIRD TERMINAL CONNECTABLE TO SAID STARTING WINDING; SAID STRIPS BEING ARRANGED TO EXTEND GENERALLY IN THE SAME DIRECTION IN LATERALLY SPACED RELATION WITH SAID FIRST BIMETAL STRIP BEING BETWEEN THE OTHER TWO STRIPS; EACH STRIP BEING SUPPORTED BY SAID SUPPORTING MEMBER AT ONE END SO THAT THE FREE ENDS OF SAID STRIPS ARE MOVABLE RELATIVE TO EACH OTHER; SAID TWO BIMETAL STRIPS EACH BEING ARRANGED TO MOVE IN A DIRECTION AWAY FROM SAID SPRING STRIP WHEN HEATED; SAID SPRING STRIP BEING BIASED TO URGE SAID FIRST CONTACT INTO ENGAGEMENT WITH SAID DOUBLE CONTACT WHEN SAID FIRST BIMETAL STRIP IS COOL AND TO URGE SAID FIRST CONTACT INTO FOLLOWING ENGAGEMENT WITH SAID DOUBLE CONTACT AS SAID FIRST BIMETAL STRIP MOVES; STOP MEANS SUPPORTED BY SAID SUPPORTING MEMBER LIMITING FOLLOWING MOVEMENT OF SAID SPRING STRIP IN A DIRECTION TOWARD SAID SECOND BIMETAL STRIP UPON MOVEMENT OF SAID FIRST BIMETAL STRIP BEYOND A PREDETERMINED POSITION; SAID FIRST BIMETAL STRIP BEING RESPONSIVE TO INITIAL CURRENT FLOW THERETHROUGH TO MOVE SAID DOUBLE CONTACT INTO CONTACT WITH SAID SECOND CONTACT; SAID SECOND BIMETAL STRIP BEING RESPONSIVE TO CUREENT FLOW THERETHROUGH TO MOVE SAID SECOND CONTACT AWAY FROM SAID DOUBLE CONTACT; SAID SECOND BIMETAL STRIP MAINTAINING SAID SECOND CONTACT SEPARATED FROM SAID DOUBLE CONTACT WHILE HEATED BYSAID FIRST BIMETAL STRIP; SAID FIRST BIMETAL STRIP BEING RESPONSIVE TO A CONTINUED ABNORMALLY HIGH CURRENT FLOW THERETHROUGH TO MOVE BEYOND SAID PREDETERMINED POSITION WHEREBY SAID DOUBLE CONTACT IS MOVED AWAY GTOM SAID FIRST CONTACT; AND SNAP-ACTING MEANS CARRIED BY SAID STRIPS TO EFFECT QUICK ENGAGEMENT AND SEPARATION OF SAID CONTACTS. 